1. Field of the Invention
The present invention relates to a raw tire forming apparatus and a raw tire forming method capable of precisely and efficiently pasting a tread ring to a raw tire base body, enhancing the uniformity of a finished tire and enhancing the productivity.
2. Prior Art
As shown in FIG. 7, in a producing step of a raw tire (tire before vulcanization) in a radial tire, it is necessary to paste a cylindrical tread ring A to a raw tire base body B which is expanded in a toroidal shape. According to a normal pasting method, a rotatable disk e which is called a tread stitcher is pushed against the tread ring A, the raw tire base body B is rotated and in this state, the disk e is gradually moved outward in the axial direction of the tire and inward in the radial direction, thereby pasting the entire tread ring A.
In the stitching method using the disk e, the carcass cord is deviated from the radial direction by twist caused by rotation torque, an angle in the lateral direction is different in the belt cord, and the uniformity of a finished tire is adversely influenced. Since the shoulder side portion of the tread ring A is gradually pushed down, it takes time for pasting the tread ring A, and the productivity of the raw tire is deteriorated.
Solutions of this problem have been proposed in patent document 1 (Japanese Patent Application Laid-open No. S60-132745), patent document 2 (Japanese Patent Application Laid-open No. 2003-71947) and patent document 3 (Japanese Patent Application Laid-open No. 2003-71948).
According to the patent document 1, however, a wide tread ring integrally provided with a sidewall rubber is used to prevent a tread edge from becoming cracked. Thus, it is necessary to crimp a wide region in the vicinity of the bead portion. Therefore, it is necessary to increase the expansion coefficient of the tube bladder, but if the expansion coefficient is increased, a large difference is prone to be generated in the expansion coefficient on the circumference, and the pasting operation can not be carried out uniformly in some cases.
In the patent document 2, since the bladder is held by a cramp member, concentric severity is high because of positional relation between the clamp body and a raw tire base body. Thus, even if there is a small deviation in concentric state, variation is generated in the cramping force, the tread edge meanders and the quality is adversely affected. Since the center of the bladder is deviated toward the tread with respect to the center of the clamp member, there is an adverse possibility that air remains below the tread ring.
In the patent document 3, since the rigidity is changed depending upon a portion of the tube, it is necessary to enhance the precision of a part of the tube and to precisely control the position where the tread ring starts abutting. Thus, it is important to form the tube precisely and to perform a high level maintenance. Since the clamp is fixed, there is a problem that concentric severity is high like the patent document 2.
In any of the patent documents 1 to 3, the step for moving the pasting apparatus to a predetermined position to crimp after the tread ring is transferred to the raw tire base body requires the same installation space and the cycle time of step as those of the conventional technique like the conventional disk.